Typical railroad cars used for load carrying operations such as hopper cars include a center sill structure which has been used in the railroad industry for many decades. The center sill structure in a railroad car includes a generally longitudinal central beam which provides the principle structural support for the entire underframe of the hopper car and allows for the transmission of the forces of draft (pulling) and buff (pushing) through a series of hopper cars. The center sill sections of such railroad cars terminate at each end in draft center sill sections. Some types of gondola cars utilize draft center sill sections without the central or through member center sill.
In any car using a draft center sill, a yoke is mounted in the draft center sill section and includes a cast yoke member having upper and lower yoke members and an internal end portion in order to form a longitudinal pocket or recess. Such yokes are well known in the industry, and have been standardized by the American Association of Railroads (AAR). Also standardized by the AAR are couplers which are mounted partially within the yoke and extend outwardly from the railroad car to couple to another railroad car. Typically, these couplers include a coupling head and a shank portion. The shank portion is connected by a pin or key to the yoke, which pin extends through an end portion of the shank of the coupler to mount the coupler for pivotal movement with respect to the yoke. The portion of the shank positioned internally of the connecting pin is known as the rear butt portion of the coupler. It is known and recommended by the AAR that a follower block be mounted between the upper and lower yoke members internally of the coupler rear butt portion to engage the rear butt portion. The follower block is mounted in this longitudinal recess between the upper and lower yoke members and serves to confine any type of resilient or spring mechanism which is positioned between the internal end of the yoke member and the follower block. In this manner, in response to draft and buff forces, particularly buff forces, the forces exerted against the coupler which are transmitted through the connecting pin and rear butt section to the follower block are evenly transmitted to the resilient mechanism or spring and thereby cushioned.
One of the problems with known follower block is that such follower blocks are rather loosely mounted within this pocket or recess between the upper and lower yoke members, and are only confined by side members of the draft sill structure. This confinement has proved to be inadequate under certain stress conditions where, in response to extreme stresses or to repeated stresses, the follower block may be pushed out of position. If the follower block is pushed out of position, the efficiency of the shock absorbent or resilient means located in the yoke recess is substantially diminished. This dislocation of follower blocks is a known problem which causes maintenance to railroad cars.
Another known problem relating to the draft gear assembly is that the yoke members themselves are pushed sideways or transversely from their longitudinal positions as a result of the same stresses applied to the coupler, which transmit through the connecting pin to the yoke. Transverse displacement of the yoke members, which are also only held in position by a part of the draft sill structure, can enhance dislocation of the follower block and can cause the yoke members to lose their longitudinal alignment which also reduces the efficiency of the cushioning mechanism located in the yoke member and can cause an entire structural deterioration of the yoke member itself due to wear of an out-of-position yoke member against the draft sill structure.
Insofar as known, these problems have not been adequately dealt with in prior draft gear assemblies. A review of certain known patents also shows that little effort has been made to solve these draft system assembly wear problems.
U.S. Pat. No. 1,947,936 of Glascodine discloses a central buffing and draft gear wherein liner plates are mounted against the side members of the center sill for purpose of absorbing lateral stress from the yoke. Such efforts to absorb the lateral stresses of the yoke member, as disclosed in the Glascodine patent, do not attempt to confine the position of the yoke member against the external forces of coupler movement. The Glascodine patent further discloses the use of front and rear follower plates which are mounted within the yoke member and extend outwardly to the side sill structure. Each of the follower plates include flange portions extending peripherally in order to provide enlarged bearing surfaces in contact with the side, liner plates which absorb shocks and prevent tendency of the follower plates to rock under stress. Thus, these peripheral flanges do not actually engage the yoke members themselves, but rather engage the side members of the side sill structure.
U.S. Pat. No. 3,599,818 of Knippel et al. discloses the use of projecting portions on a rear wall member which also engages a resilient mechanism within the center sill. The projecting portions in Knippel are for the purpose of confining a spring part of the resilient mechanism and mounting additional external absorbing elements, and do not engage or maintain the rear block in position with respect to a yoke.
Other patents generally disclosing follower blocks include U.S. Pat. No. 4,593,827 of Altherr which discloses a generally rectangular follower block which engages the rear butt portion of a draw bar and is held in position within a pocket casting. U.S. Pat. No. 2,386,476 of Kinne et al. also discloses a follower block mounted within the pocket of a casting. U.S. Pat. Nos. 4,531,648 of Paton; 3,716,146 of Altherr; and 4,480,758 of Hurt disclose various embodiments of follower blocks. U.S. Pat. No. 4,311,765 of Chung discloses a polyurethane shock absorbing unit to be used inside a draft gear as a primary shock absorbing medium within the gear.
In summary, there is no known solution for the problem of migration of the draft gear follower block and the wear problems associated with transverse or sideways movement of the yoke itself in response to the external stresses placed upon the coupling element. The result of these stresses is that the follower blocks lose position potentially causing undue wear. There is additional undue wear that can be caused by the yoke being moved out of position or being subjected to transverse agitation. The only known way to repair these problems is to take a railroad hopper car out of commission, replace the parts and/or building up through weld the effected wear areas, all of which is extremely time-consuming and expensive.